Optical switch with mobile components and method for making same

ABSTRACT

Optical switch comprising optical means ( 120 ) and driving means ( 114, 115, 124 ) on a substrate ( 100 ), cooperating with optical means to make them pivot between a rest position and at least one active position. According to the invention, the switch comprises first mobile stop means ( 122 ), rigidly fixed to the optical means ( 120, 130 ) so that they can pivot with the optical means, and second fixed stop means ( 128 ) arranged in a plane approximately parallel to the main face ( 110 ) of the substrate and cooperating with the first stop means, to fix the said active position of the optical means.  
     Application to make an optical cross connect.

TECHNICAL DOMAIN

[0001] This invention relates to an integrated optical switch withmoving parts, an optical cross connecting device using the switch, and aprocess for making the switch.

[0002] Optical cross connecting devices can be compared withmultiplexers capable of optically selectively connecting one or severaloptical input channels to one or several output channels. They useoptical switches for this purpose.

[0003] The invention also relates to on/off type switches, in otherwords switches that enable or disable the passage of light, and switchesthat reflect light, or switches that modify a characteristic of light.The switches may have two or more switching states.

[0004] Many applications of the invention are in the field of opticaltelecommunications and optical signal processing.

STATE OF PRIOR ART

[0005] Documents (1), (2) and (3) for which the complete references aregiven at the end of the description, give an illustration of atechnological background of the invention.

[0006] Document (1) describes a multichannel optical switch equippedwith a flexible distribution beam. This beam is provided with an opticalmicroguide, and distributes a light beam applied at an input channel toone output channel selected among several possible output channels.

[0007] The use of this type of switch to make an optical cross connectnecessitates a large number of components, and therefore a large numberof electronic control circuits for these components. Furthermore, theswitch creates large optical losses.

[0008] A smaller number of components may be used in an optical crossconnect of the “in free space” type. In this type of cross connect, forexample described in document (2), switches with vertical “torsion”mirrors are used.

[0009] The vertical mirrors may occupy a first switching positioncorresponding to a light reflection mode, and a second switchingposition corresponding to a light transmission mode.

[0010] The mirrors are placed perpendicular to a main face of a supportsubstrate. They may pivot about an axis which is also perpendicular,between two switching positions. The mirrors are moved by applyingelectrostatic forces between a mirror support plate and a verticalelectrode.

[0011] In this type of switch, control of the verticality of the mirrorsmay be critical. A verticality fault of a mirror may cause misalignmentof the optical beam reflected by the mirror.

[0012] Document (3) also describes a switch in which a mirror is pivotedby electromagnetic forces from a rest position parallel to thesubstrate, towards an active position perpendicular to the substrate. Inthis case also, there is the problem in keeping the mirror in its activeposition while guaranteeing that this position can be maintained withprecision.

PRESENTATION OF THE INVENTION

[0013] The purpose of this invention is to propose an improved opticalswitch that does not have the difficulties mentioned above and in whichthe active position of a mirror or another optical means may be fixedprecisely.

[0014] Another purpose is to propose a switch that may be an on/off typeswitch but that can also be designed to have several switching states.

[0015] Another purpose is to propose a particularly simply and economicprocess for making such a switch.

[0016] Finally, another purpose of the invention is to propose anoptical cross connecting device using the improved optical switch.

[0017] More precisely, the objective of the invention to achieve thesepurposes is an integrated optical switch comprising optical meanscapable of interacting with a switching light, and driving meansconnected to the optical means to make them pivot between a first “rest”position and a second “active” position, all fixed on a substrate.According to the invention, the switch comprises first mobile stop meansrigidly fixed to the optical means, so that they can pivot with theoptical means, and second fixed stop means arranged in a planeapproximately parallel to the main face of the substrate and cooperatingwith the first stop means to fix the said active position of the opticalmeans.

[0018] The driving means may be electrostatic means or electromagneticmeans.

[0019] The pivot axis of the optical means and of the first stop meansis preferably parallel to the main face of the substrate.

[0020] Since the fixed stop means are parallel to the main face of thesubstrate, it is possible to adjust the position of the fixed stop meansvery easily and very precisely. Since the mobile stop means are rigidlyfixed to the optical means, the active position of the optical means isalso precisely fixed by adjustment of the fixed stop means.

[0021] Since the fixed stop means according to the invention may beparallel to the main plane, the precision at which these means areformed is related to the precision of the layer thicknesses. On theother hand, in prior art, these stop means were made by the wall of therecess in the substrate which was perpendicular to the plane of thesubstrate, and the precision of the position of the optical means wasthen dependent on the precision of the assembly. This is not the case inthe invention.

[0022] According to a particular embodiment of the switch, there may bean angular spacing between the mobile stop means and the optical means.Due to the rigid link between the mobile stop means and the opticalmeans, this angle is not changed during the pivoting movement of theoptical means.

[0023] Thus in the invention, the optical function and the positioningfunction are dissociated, which is not the case in prior art in whichthe optical means and the mobile stop were in a parallel plane.

[0024] Due to the angular spacing, the stop means are not located in thesame plane as the optical means. More precisely, the stop means areoutside a plane parallel to a plane containing the optical means in theactive position. Therefore, there is no risk of interaction with lightand there is no need for a particular antireflection treatment toprevent parasite reflection.

[0025] For example, the angle formed by the mobile stop means and theoptical means may be a right angle. In this case, if the main face ofthe substrate comprises fixed stop means, the optical means may beswitched such that the optical means extend approximately parallel tothe main face of the substrate when in the rest position, and theoptical means are approximately perpendicular to the main face of thesubstrate in at least one of the active positions.

[0026] According to another particular aspect of the invention, thedriving means may comprise at least one first electrode called themobile electrode fixed to the optical means so that they can pivot withthe optical means, and at least one second electrode called the fixedelectrode, fixed to the substrate. A fixed electrode is associated witheach mobile electrode, to apply electrostatic pivoting forces betweenthe mobile electrode and the associated fixed electrode.

[0027] Advantageously, the first stop means, in other words the mobilestop means fixed to the optical means, may form one or several mobileelectrode(s) or may carry one or several mobile electrode(s). The stopmeans then also perform the function of activating the optical means.

[0028] In the special case in which there is an angular spacing betweenthe stop means and the optical means, it is possible to separate theelectrode plane from the optical means plane, and thus release opticalmeans from constraints related to the presence of an electrode. Thisenables a wider choice of the optical means.

[0029] In particular, the optical means may comprise one or severaloptical components, for example chosen from among a mirror, a separatingstrip, a lens, a strip of absorbent material and a strip of reflectingmaterial, and a diffractive lens.

[0030] When the driving means are of the electromagnetic type, theelectrodes are replaced by magnetic coils.

[0031] In a more sophisticated embodiment of a switch with severalactive positions, the optical means may have a first part with a firstoptical property upright on the substrate in a first active position,and a second part with a second optical property different from thefirst optical property or the same as the first optical property,upright on the substrate in a second active position.

[0032] These optical means and the mobile stop means may be pivoted byhinge means connecting them to the substrate.

[0033] The hinge means may for example comprise one or several torsionbeams extending approximately along the pivot axis.

[0034] The torsion beams may also automatically return the optical meansinto either the active position or the rest position.

[0035] The invention also relates to an optical cross connecting devicecomprising several optical switches like those described above arrangedin lines and rows, an optical input channel being associated with eachline or row, switches and an optical output channel being associatedwith each row or line of switches.

[0036] The optical cross connecting device may also comprise severaloptical fibres coupled to the corresponding lines and rows of opticalswitches. Each fibre is thus associated with an input channel or anoutput channel of the device.

[0037] The invention also relates to a process for making a switch likethat described. The process comprises the following steps in sequence:

[0038] a) the formation of at least one fixed electrode on a main faceof a first substrate, and definition of optical means on a secondsubstrate, parallel to a main face of the second substrate,

[0039] b) assembly of the fist and second substrates, by putting thesaid main faces facing each other and

[0040] c) etching of the second substrate by a free rear face oppositethe main face, to form at least one mobile stop in the substrate,rigidly fixed to the optical means, and to release the optical means.

[0041] The mobile stop formed in the second substrate may act as asupport for the mobile electrode or may form a mobile electrode itselfwhen the substrate material is not insulating. A non-insulating materialis a conducting material or a semiconducting material to which anelectrical potential may be applied that can generate the electrostaticforce necessary to pivot the optical means.

[0042] Note also that several stops and/or several mobile electrodes maybe formed simultaneously or not simultaneously.

[0043] Step a) in the process may also comprise etching of at least onecavity for reception of the optical means in the first substrate.

[0044] The cavity holds optical means, particularly in their restposition, such that they completely release a space for passage of thelight beam to be switched.

[0045] Furthermore, step a) in the process may include the definition ofone or several fixed stops in the first substrate, cooperating with themobile stop in the second substrate, to fix a position of the opticalmeans in the active position and/or the rest position.

[0046] The fixed stops form fixed stop means and give a betterdefinition of the active or rest position of optical means. If there areno stops, the fixed stop means may simply be formed by the surface ofthe main face of the first substrate.

[0047] Other characteristics and advantages of the invention will becomeclearer from the description made with reference to the figures in theattached drawings. This description is provided purely for illustrativepurposes and is in no way limitative.

BRIEF DESCRIPTION OF THE FIGURES

[0048]FIG. 1 is a partial exploded diagrammatic view of an opticalswitch according to the invention.

[0049]FIG. 2 is a diagrammatic section along a plane I-I of the switchin FIG. 1.

[0050]FIG. 3 is a diagrammatic section of a switch forming a variantwith respect to FIG. 2.

[0051] FIGS. 4 to 6 are diagrammatic sections of substrates prepared forthe formation of a switch according to the invention.

[0052]FIG. 7 is a diagrammatic representation of substrates preparedaccording to FIGS. 4 to 6 in a state preceding their assembly.

[0053]FIGS. 8 and 9 are diagrammatic sections of substrates after theirassembly, and illustrate subsequent steps in a process for the formationof the switch according to the invention.

[0054]FIG. 10 is a top view of a diagrammatic and simplifiedrepresentation of an optical cross connecting device including opticalswitches according to the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

[0055] In the following description, identical, similar or equivalentparts in the different figures are marked with the same references, tosimplify reading. Furthermore, the figures are not all at the same scalefor reasons of clarity.

[0056] The switch in FIG. 1 comprises a first substrate 100 with a mainface 110.

[0057] The main face has a depression 112 in which the fixed electrodes114 are formed.

[0058] The depression 112 is designed to contain a mirror 120 in a restposition. In this example, the mirror 120 forms the optical means in thesense of the invention.

[0059] The mirror is rigidly connected to two ribs 122 located on eachside of the mirror. In the example shown, these form a right angle withthe plane of the mirror.

[0060] The ribs are placed facing the fixed-electrodes 114 and carryelectrodes 124 called mobile electrodes on their face facing towards thefixed electrodes.

[0061] The ribs 122 do not need any electrodes and form the electrodesthemselves when they are made from a non-insulating material.

[0062] Torsion beams 126 connect the assembly formed by the mirror 120and the ribs 122 to a fixed part of the substrate 100. They enablepivoting of the mirror and the ribs about an axis parallel to the mainface 110. This axis is materialized by beams 126 that form a hinge.

[0063] In this respect, it should be specified that the beams 126 arefree with respect to the bottom of the depression 112. They are onlyconnected to the fixed part of the substrate at their ends shown by theletter P in FIG. 1. Note also that the mirror 120 and the beams 126 areetched in thin layers 201, 202 inserted between the first substrate 100and a second substrate 200. This point is not shown in FIG. 1, but itwill be described in more detail in the remainder of the text withreference to the following figures.

[0064] When no potential difference is applied between the mobileelectrodes 124 and the fixed electrodes 114, or when the potentialdifference is less than a switching threshold, the mirror occupies thebottom position shown in the figure in which it rests in the depression112.

[0065] In this case, a light beam may pass above the substrate along apath materialized by an arrow F₁ in the figure. The beam passes througha free switching space 220 and in a first output groove 222 formed inthe second substrate 200.

[0066] The state in which a beam can follow the path along arrow F1, isa first switching state called the rest state.

[0067] When a potential difference greater than a switching threshold isapplied between the mobile electrodes 124 and the fixed electrodes 114,the assembly formed by the ribs 122 and the mirror 120 pivots in adirection indicated by small arrows. Pivoting is caused by a rotationtorque that is generated from electrostatic forces exerted between themobile electrodes and the fixed electrodes. This rotation torque mustovercome a return torque exerted by the torsion beams 126.

[0068] The switching threshold may be determined experimentally or bycalculation, and it depends essentially on the surface of theelectrodes, their conductivity, their spacing and the return torque ofthe torsion beams.

[0069] The mirror stops pivoting when the ribs 112 stop in contact withthe main face 110 of the first substrate 100. In the example in thefigure, the main face is equipped with stops 128 called “fixed stops”that cooperate with the ribs to more precisely fix the position of themirror in its upright position. Thus, the ribs form mobile stop meanslike those described previously. The fixed stop means are formed by themain face of the first substrate, or by fixed stops when it is equippedwith them.

[0070] When the ribs are bearing against the stops 128, the mirroroccupies the upright or “active” position (not shown) in which a lightbeam may be reflected along a direction indicated by an arrow F₂ indashed lines.

[0071] In the example illustrated, this state is a second switchingstate called the “active state”.

[0072] The assembly formed by the mobile electrodes and fixed electrodesforms part of the driving means mentioned above.

[0073]FIG. 2 is a simplified diagrammatic section of the device in FIG.1 according to the plane I-I shown in FIG. 1.

[0074] It shows the mirror 120 and a rib 122 in an intermediate positionbetween the rest position and the active position, in solid lines. Italso shows these parts in the active position in dashed lines.

[0075] It may be observed that the stops 128 of the main face of thesubstrate 110 have an adjusted height such that the mirror 120 isperpendicular to the said face in the active position.

[0076] In this position, the rib 122 is parallel to the main face of thesubstrate.

[0077] In other applications, other active positions are defined bydifferent height of the stops, or an angle between the ribs and themirror not equal to 90°.

[0078] It can also be observed that the mirror 120 is formed of asupport 119 and a layer of reflecting material 121 covering a face ofthe support. The support 119 is composed of two intermediate layers 201,202 already mentioned.

[0079] Other elements, for which the references are marked in thefigure, are identical to those already described with reference toFIG. 1. Therefore, the reader should refer to this description.

[0080]FIG. 3 shows another possibility for making a switch according tothe invention.

[0081] In the example in FIG. 3, the optical means comprise a firstoptical component, actually the mirror 120, extending from one of thesides of the ribs 122 (only one is visible) and another opticalcomponent 130, for example a semi-transparent strip or a second mirror,extending on a side opposite the ribs 122.

[0082] Similarly, the first substrate 100 has a set of first fixedelectrodes 114 and a set of second fixed electrodes 115 arranged on eachside of the ribs and the torsion beams 126.

[0083] Note that the ribs 122 do not have any electrodes. They are madefrom a non-insulating material, such that they also form mobileelectrodes.

[0084] Note also that the first substrate is provided with a groove 102in which the optical means are free to move.

[0085] When no voltage is applied between the electrodes, in other wordsin the rest switching state, the two optical components 120, 130 are ina position approximately parallel to the main face 110 of the firstsubstrate 100. The ribs 122 are then perpendicular to the substrate.This position corresponds to the rest position, in which the system isautomatically returned by the torsion beams 126.

[0086] In a first active switching state, a voltage is applied betweenthe ribs 122 which form the mobile electrodes, and the first fixedelectrodes 114. The assembly formed by the ribs and the optical meansthen pivots about the axis of the torsion beams 126 until the ribs comeinto contact against the stops 128 placed close to the first fixedelectrodes 114.

[0087] The first optical component 120 is then arranged in the freeswitching space 220 in which it can act on a light beam. The secondoptical component 130 fits into the movement groove 102 of the firstsubstrate 100.

[0088] In a second active switching state, a switching voltage isapplied between the ribs 122 and the second fixed electrodes 115. Theassembly formed by the ribs and the optical means then pivots in theopposite direction until the ribs 122 come into contact with the stops129 placed close to the second fixed electrodes 115. In this state thesecond optical component 130 moves into the free switching space 220 andthe first optical component drops into the movement groove 102.

[0089] For example, a device conform with FIG. 3 may be used in anoptical cross connect in which it is required to distribute light poweronto several output channels.

[0090] The mirrors can then be replaced by partially reflecting strips.

[0091] The reference 300 diagrammatically indicates the electroniccontrol means provided to apply switching voltages to the electrodes.These means as such are not included in the invention and are notdescribed herein. They can be made using usual techniques inmicroelectronics or electronics.

[0092] As in the previous figures, FIG. 3 shows that the first andsecond substrates may be separated by two intermediate layers 201, 202.The origin of these layers will appear in the remainder of the textdescribing a process for manufacturing the optical component.

[0093]FIG. 4 shows a sectional view of the preparation of the firstsubstrate 100 during a process for manufacturing of a switch accordingto the invention. For example, it may be a silicon substrate in whichthe main face 110 is etched to form a depression 112 and possibly stops128. The stops 128 delimit a region for the formation of fixedelectrodes.

[0094] The fixed electrodes 114, only one of which is visible, areformed by deposition and etching of a metallic layer such as a goldlayer.

[0095] The metallic layer may be electrically isolated from thesubstrate, if the substrate is conducting. The insulation may be made bydepositing an intermediate layer such as silicon oxide.

[0096] Similarly, electrical conducting tracks (not shown) are formed toconnect the electrodes to the electronic control means 300 mentioned inrelation with FIG. 3.

[0097]FIG. 5 shows a section through a substrate 200 that can be used toform the second said substrate of the switch.

[0098] The substrate 200 has a thin surface layer 201 and a thin buriedlayer 202, made from a material different from the material on thesurface layer. The buried layer 202 separates the surface layer 201 froma solid part 203 of the substrate.

[0099] The substrate 200 may for example be of the Silicon On Insulator(SOI) type, which consists of a thin layer of silicon, a buried layer ofsilicon oxide and a solid part made of silicon, in order.

[0100] The surface layer 201 and the buried layer 202 are shaped usingtypical photolithography and etching techniques, to define and surrounda plate that will form, or at least support, the optical means of theswitch. As shown in FIG. 6, the plate is provided with a reflectingmetallic layer 121, and thus forms a mirror. By analogy to the previousfigures, the plate forming the mirror is marked as reference 120 and isdenoted as a “mirror”.

[0101] Etching of the surface and buried layers 201 and 202 is alsouseful to define the torsion beams 126 that prolong the plate (strip) ofthe mirror. It is also useful to form a depression 212 at the mainsurface 210 of the second substrate 200. The depression 212 is locatedin a region approximately symmetrical with the region containing themirror, with respect to beams 126.

[0102]FIG. 7 shows a perspective view of the projection of the secondsubstrate 200 on the first substrate 100 just before they come intocontact.

[0103]FIG. 7 gives a better view of the shapes and locations of thetorsion beams 126 and the mirror 120 defined on the second substrate,and the shapes and the positions of electrodes 114 and stops 128 on thefirst substrate.

[0104] In particular, it may observed that the position and dimensionsof the depression 112 of the first substrate 100 are provided to containthe mirror 120 and the torsion beams 126 of the second substrate 200. Inparticular, the depression prevents bonding contact between the firstsubstrate and the torsion beams and the mirror. This prevents thesebeams from bonding on the first substrate 100.

[0105] Similarly, the depression 212 in the second substrate 200 isdesigned to coincide with the electrodes 114 and the stops 128. It alsoprevents these parts from bonding together.

[0106] The main faces 110 and 210 of the first and second substratescome into contact around their peripheral part without any relief, tocause bonding. This bonding may be direct molecular bonding (“waferbonding) or bonding using a binder.

[0107]FIG. 8 shows a sectional view of the structure obtained afterbonding, along a plane VII-VII shown in FIG. 7.

[0108] It may be observed that the first and second substrates are onlyfixed around part of their periphery, in other words a part in whichthere are no optical means or driving means.

[0109] A final step illustrated in FIG. 9 comprises deep etching of thesecond substrate 200 through a free face of this substrate. It is the“back” face opposite the main face 210.

[0110] Etching defines the ribs 122, clears the free switching space 220and releases the mirror 120.

[0111] Anisotropic type etching is done using the buried layer 202 asthe etching stop layer to protect the mirror 120.

[0112] Furthermore the ribs, preserved during etching are connected tothe mirror through the buried layer 202 and are located vertically inline with the torsion beams 126. The position and the shape of the ribsmay be fixed by an etching mask not shown.

[0113]FIG. 9 is also similar to FIG. 2 described above.

[0114] The buried layer 202 on the mirror 120 exposed during etching,may be eliminated if necessary.

[0115] The above description refers to the manufacture of a singleswitch. However, several switches may be made simultaneously on the samesubstrate.

[0116] As an illustration, FIG. 10 shows an optical cross connect 10using several optical switches like those described above. Theseswitches, for example with mirrors, are marked as reference 20 and aremarked by a cross when in the active state.

[0117] The optical cross connect has several input channels coupled toseveral optical signal input fibres 12. For example, coupling can takeplace through a network of lenses 14.

[0118] Similarly, the cross connect is coupled to several optical signaloutput fibres 16, through a second network of lenses 18. Each fibre 14materializes a cross connect output channel.

[0119] The optical switches 20 are distributed in lines and in rows,each line being associated with an input channel and each row beingassociated with an output channel.

[0120] When a switch is in an active switching state, its upright mirrorfor example reflects a beam F received from a signal input fibre to asignal output fibre. The input channel may thus be selectively coupledto the output channels.

DOCUMENTS MENTIONED

[0121] (1) FR-A-2 660 444

[0122] (2) “2×2 MEMS FIBER OPTIC SWITCHES WITH SILICON SUB-MOUNT FORLOW-COST PACKAGING”by Shi-Sheng Lee et al. Solid-State Sensor andActuator Workshop, Jun. 8-11, 1998, pages 281-284.

[0123] (3) “ELECTROMAGNETIC TORSION MIRRORS FOR SELF-ALIGN FIBER-OPTICCROSS CONNECTORS BY SILICON MICROMACHINING” by Hirashi Toshiyoshi etal., IEEE Journal of selected topics in quantum electronics, vol. 5, No.1, 1999, pages 10-17.

1. Optical switch comprising optical means (120, 130) on a substrate(100, 200) capable of interacting with switching light, and drivingmeans (114, 115, 124) cooperating with the optical means to make thempivot between a first “rest” position and at least one second “active”position, first mobile stop means (122) rigidly fixed to the opticalmeans (120, 130) so that they can be pivoted with the optical means, andsecond fixed stop means (128) formed in a plane approximately parallelto the main face (110) of the substrate and cooperating with the firststop means to fix the said active position of the optical means, thisswitch being characterized in that it is integrated, the first stopmeans (122) and the optical means (120, 130) are connected to thesubstrate (100, 200) by a torsion beam (126) extending along a pivotaxis forming a single assembly with the torsion beam (126), the angularspacing between the first stop means (122) and the optical means (120)being approximately a right angle, and that in the rest position, theoptical means (120) extend approximately parallel to the main face (110)of the substrate (100).
 2. Switch according to claim 1, in which thedriving means comprise at least one electrode (124) said to be mobile,fixed to the optical means (120) so that it can pivot with the opticalmeans, and at least one electrode (114) said to be fixed, that isrigidly attached to the substrate, associated with a correspondingmobile electrode to exert electrostatic pivoting forces between eachmobile electrode and the corresponding fixed electrode.
 3. Switchaccording to claim 2, in which the first stop means (112) form at leastone mobile electrode.
 4. Switch according to claim 2, in which the firststop means carry at least one mobile electrode (124).
 5. Switchaccording to claim 1, in which the optical means (120, 130) comprise atleast one of several means among a mirror, a separating strip, a lens, aplate of an absorbent material, and a plate of reflecting material. 6.Switch according to claim 1, in which the optical means have a firstpart (120) with a first optical property upright on the substrate in afirst active position and a second part (130) with a second opticalproperty, different from or the same as the first optical property,upright on the substrate in a second active position.
 7. Optical crossconnecting device (10) comprising several optical switches (20)according to claim 1, arranged in lines and rows of optical switches, anoptical input channel being associated with each line or each row ofswitches and an optical output channel being associated with each row orline of the switch.
 8. Cross connecting device according to claim 7,comprising several optical fibres (12, 16) coupled to the lines and rowsof optical switches, respectively.
 9. Cross connecting device accordingto claim 1, characterised in that the substrate is divided into twoparts attached by plane contact faces, one of the parts carrying thesecond stop means (128) and the other carrying parts supporting theassembly consisting of the torsion beam (126), the first stop means(122) and the optical means (120, 130).
 10. Process for manufacturing anoptical switch comprising optical means (120, 130) capable ofinteracting with switching light and driving means (114, 115, 124)cooperating with the optical means to make them pivot between a first“rest” position and at least a second “active” position, on a substrate(100, 200), the first mobile stop means (122) rigidly fixed to theoptical means (120, 130) so that they can pivot with the optical means,and second stop means (128), fixed and arranged in a plane approximatelyparallel to the main face (110) of the substrate, and cooperating withthe first stop means to fix the said active position of the opticalmeans, comprising the following steps in sequence: a) the formation ofat least one fixed electrode on a main face (110) of a first substrate(100), and definition of optical means (120) on a second substrate(200), parallel to a main face (210) of the second substrate, b)assembly of the first and second substrates, by putting the said mainfaces (110, 210) facing each other, c) etching of the second substrate(200) by a free rear face opposite the main face, to form at least onemobile stop (122) in the substrate, rigidly fixed to the optical means(120), and to release the optical means.
 11. Process according to claim10, in which a second substrate made from a non-insulating material isused such that the stop (122) forms an electrode.
 12. Process accordingto claim 10, also comprising the formation of an electrode (124) on thestop.
 13. Process according to claim 10, in which step a) also comprisesetching of at least one cavity (112) in the first substrate (100), tocontain the optical means.
 14. Process according to claim 10, in whichthe step a) also comprises the definition of at least one fixed stop(128) in the first substrate, cooperating with the mobile stop (122)formed in the second substrate, to fix a position of the optical meansin the active position and/or the rest position.
 15. Process accordingto claim 10, in which a second substrate (200) is used with a surfacelayer (201) separated from a solid part (203) by a buried layer (202)and in which a plate forming the optical means (120) and torsion bars(126) connecting the plate to a fixed part of the surface layer aredefined by etching in the surface layer.
 16. Process according to claim15, in which a layer of an optical material (121) is deposited on thesurface layer in a region in which the said plate is defined. 17.Process according to claim 15, in which step c) includes etching of thesecond substrate with a stop on the buried layer (202).
 18. Processaccording to claim 15, in which the second substrate (200) is of the SOI(Silicon On Insulator) type.
 19. Process according to claim 10, in whichat least one groove (102) is etched to enable movement of the opticalmeans in the first substrate (100).